Shooting SS109 gives the issues, not all the tiime, but some. A buddy gave me a mag of ADCOM M855 and it ran like a top w/out hiccup. Here's my question; rifle only has 200 rounds through it as of this posting, should I not sweat it until about 500 rounds and give it a chance to break it/seat?

Ran 180 more rounds through this rifle and the thing would still short stoke on occasion. Took it to John Axe @ Gun R/X (Cache Creek Fly Shop, if you're anywhere near Lawton, OK, John's a great smith) and talked about my problems...we proceded to tear the rifle apart and swapped the original recoil spring (from an older Bushmaster, mic'd at .075) for a new spring (mic'd at .069) and lo and behold...rifle runs like a raped ape now.

Seems that the larger diameter spring was giving too much sproing...

May be something good to check out it you've got short stroking issues on a new build.

If you get the chance, see if you can get the old spring back for a back up.

It could be that the rifle is still breaking in (rough anodized parts self polishing out), and once the rifle is broken in, it could start having excessive recoil from the weaker recoil spring (impact of the buffer off the back of the receiver extension).

Regarding wire gauge size, it's one of the factors for overall tension, but so are spring winding and the treatment of the wire it's self. To verify a springs tension weight, you need a spring tension gauge, and not base the tension on wire gauge, coil winding, nor length alone.